Catechins are known to have inter alia a suppressing effect on an increase in cholesterol level and an inhibitory effect on α-amylase activity (for example, JP-A-60-156614 and JP-A-03-133928). To have such physiological effects of catechins developed, it is necessary for an adult to drink 4 to 5 cups of tea in a day. Accordingly, there is an outstanding desire for technology that permits the addition of catechins at high concentration in beverages to facilitate the ingestion of a large amount of catechins.
In tea leaves, however, caffeine components are also contained generally at from 2 to 4% although catechins are contained as much as about 15%. As caffeine exhibits a central nervous system stimulant effect, it is used for the suppression of sleepiness. On the other hand, its excessive ingestion is said to become a cause of induction of adverse effects such as nervosity, nausea and hyposomnia. Thus investigations have been made about processes that can selectively remove only caffeine from caffeine-containing compositions.
As decaffeination processes of coffee, for example, there have been proposed a process that coffee is brought into contact with a caffeine adsorbent such as activated carbon under from 150 to 250 atm (JP-A-53-18772) and a process that caffeine is selectively removed by bringing a caffeine-containing, aqueous solution into contact with activated clay or acid clay (JP-A-06-142405).
However, the former relates to a supercritical extraction technique, so that it requires substantial investment on process equipment and lacks readiness in its practice on an industrial level. This process also involves a problem in that it achieves not only selective removal of only caffeine but also results in a modification to the composition of catechins as effective ingredients. The latter process, on the other hand, is accompanied by a problem in that the hue may deteriorate in some instances, although caffeine can be selectively removed by simply using activated clay or acid clay.